The present invention concerns friction clutches, notably for motor vehicles, including on the one hand a clutch engagement device comprising a diaphragm bearing on a cover, fixed to a flywheel for driving in rotation, for action on a thrust plate and clamping the friction linings of a friction disc between the thrust plate and the driving flywheel and on the other hand a linkage for acting in an opposing fashion on the internal end of the diaphragm, an actuator for controlling the said linkage, and an adjustment device, referred to as a device for taking up wear, for compensating for the wear on the friction linings, in which the actuator has manoeuvring means with an electric motor, a mechanical transmission with an input element formed by the output shaft of the electric motor, an output element for acting on the linkage, elastic assistance means acting between a fixed part and an element of the transmission in order to act in an opposing fashion with respect to the diaphragm so that the electric motor provides only a small force for disengaging the clutch.
For example (FIG. 1) the actuator has an electric motor 50 acting on a mechanical transmission 60 having pinions and a toothed sector to which is attached a coil spring 70 constituting the elastic assistance means.
The linkage 80 has a fork connected to the toothed sector and a clutch release bearing acting on the internal end of the fingers of the diaphragm mounted pivotally on the base of the cover 2 by means of assembly means 8 having a primary support formed by pressing in the base of the diaphragm and a spring ring forming a secondary support opposite the primary support.
The spring ring, in a known fashion, is carried by lugs formed by cutting and bending in the base of the cover, the said lugs passing through the diaphragm 3 having in a known fashion a peripheral part in the form of a Belleville washer extended radially inwards by a central part divided into radial fingers by slots. The Belleville washer constitutes the clutch engagement means, whilst the radial fingers form the clutch disengagement means.
The external periphery of the diaphragm 3 bears on the thrust plate 1 in order to clamp the friction linings of the friction disc 6 between the thrust plate 1 and the driving flywheel 102 fixed, in a manner which cannot be seen, to a driving shaft, whilst the friction disc 6 has centrally a fluted hub cooperating with the flutes on a driven shaft 101 passing through the aforementioned clutch release bearing. Thus referred to the clutch release bearing, the characteristic curves of FIG. 2 are obtained, in which the X-axis C corresponds to the travel of the clutch release bearing in mm and the Y-axis E to forces in newtons.
The curve A corresponds to the load on the clutch release bearing, the curve B to the opposing load of the elastic assistance means and the curve D to the force developed by the electric motor.
The elastic assistance means store the energy of the diaphragm 3 during the clutch engagement operation and restores it, usually more quickly, at the time of the declutching operation.
Thus the electric motor supplies only the difference between the force of the diaphragm and the force of the elastic assistance means.
In addition, as described in the document FR-A-2 564 921, a device for taking up wear is provided, making it possible to reduce the travel of the elastic assistance means, thus affording excellent behaviour of these elastic means, which can thus be located conveniently in the actuator.
Nevertheless it may be desirable to reduce the cost of the actuator still further and to simplify the latter still further whilst having a robust and compact design.
The object of the present invention is to meet these requirements.